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Since an explanation could not yet be found for this phenomenon. I have plotted two graphs to show the effect.

https://www.dropbox.com/s/5e8xrrctu0rcwx3/CPU%20scaling%20%20-%20continuous%20vs%20increasing%20from%201.png?dl=0
https://www.dropbox.com/s/txpkb8k6mpyexv8/CPU%20scaling%20-%20increase%20from%201.png?dl=0

The first graph shows the VM CPU resize time (y axis) vs number of vCPUs (x axis) of continuous (blue) and resize from a VM with 1 vCPU (green) scenarios.The second graph shows the VM CPU resize time (y axis) vs number of vCPUs (x axis), when resized from a VM with 1 vCPU at each step (The green line in first graph). The error bars show the standard error of the gathered values at each step, as I did resize multiple times to get a mean value.

Can anyone give an explanation for this?

> On 26 Jul 2016, at 11:30, Chathura M. Sarathchandra Magurawalage <77.chathura at gmail.com> wrote:
> 
> Thanks Tomas.
> 
> Yes you are right but that will only happen when you resize disk at each step. But when I increased CPU other resource were kept fixed. So in This case, it won’t be copying bigger disk over each time.
> 
> 
>> On 26 Jul 2016, at 08:45, Tomas Vondra <vondra at czech-itc.cz> wrote:
>> 
>> Chathura M. Sarathchandra Magurawalage <77.chathura at ...> writes:
>> 
>>> 
>>> Hi, 
>>> 
>>> Does anyone know the reason for VM resizing time to increase faster if you
>> continuously increase CPU or DISK
>>> resources by +1 (e.g. 1-2, 2-3, 3-4, 4-5). Whereas, when you increase from
>> 1 to any of +1/+2/+3/+4…..+n
>>> (e.g. 1-2, 1,3, 1-4, 1-5), the VM resize time still increases at each
>> step, but it takes less time in
>>> comparison to the former method. Can anyone give an explanation for this? 
>>> 
>> 
>> Hi!
>> If I'm correct, the resize operation stops the VM, migrates it to another
>> computed node and starts it with another configuration there.
>> So if you have your VM running on local storage, moreover raw local storage,
>> you will be copying a bigger disk over each time. Otherwise, it should not
>> matter. Am I correct about your configuration?
>> Tomas
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>